1. Field of the Invention
The present invention relates to a motor controller, and more specifically relates to a motor controller having the function of determining or modifying a condition for detecting a power failure of a power supply.
2. Description of Related Art
In cases of power failure that prevents the continuation of the normal operations of motor controllers and peripheral devices thereof, machines using the motor controllers are failed. Thus, the motor controllers generally include power failure detection means and perform protection operations to stop the machines before the continuation of the normal operations is hindered.
The amount of energy that is required for continuing the normal operations of the motor controller and the peripheral devices thereof, in cases of power failure, is referred to as a “power failure tolerance”. The upper limit of time to detect a power failure is defined as an “upper limit regulation time”. A voltage to detect a power failure by a reduction in a power supply voltage is defined as a “regulation voltage”. Although the upper limit regulation time and the regulation voltage depend on the “power failure tolerance”, the “power failure tolerance” varies from machine to machine. Thus, the upper limit regulation time and the regulation voltage are each required to be determined differently from machine to machine.
Therefore, a method for selectable switching a regulation time among a plurality of time threshold values by an electric selection circuit provided in a motor controller is proposed (for example, Japanese Patent No. 5283752, hereinafter called “patent document 1”). In the invention described in the patent document 1, a voltage threshold value and the time threshold value are defined as a power failure detection threshold value. A control voltage during a power failure varies differently depending on whether or not a motor acts as a generator. Thus, the patent document 1 proposes a method for selectable switching the detection threshold value from the two detection threshold values using the electric selection circuit.
Also, a motor control method in which when a detected power supply voltage is equal to or lower than a predetermined threshold value, the power supply is determined to be shut down and the operation state of a motor at the time of the shutdown is stored in a nonvolatile memory device is proposed (for example, Japanese Unexamined Patent Publication (Kokai) No. 2004-229410, hereinafter called “patent document 2”). In this method, a threshold value is varied depending on a load of the motor. However, the patent document 2 does not disclose a threshold value associated with time.
Also, a method in which the relationship between a power failure tolerance and a voltage amplitude is measured to detect a power failure is known (for example, Japanese Unexamined Patent Publication (Kokai) No. 2011-155803, hereinafter called “patent document 3”). However, the patent document 3 does not concretely describe a means for changing the relationship between the power failure tolerance and the voltage amplitude, though the relationship between the power failure tolerance and the voltage amplitude varies from machine to machine.
As described above, since the “power failure tolerance” is different from machine to machine, the conventional techniques that store a number of detection results and perform switching require complicated circuit configurations. This causes an increase in cost and size of a motor controller.